Electrodeposition of copper and copper alloys



United States Patent ELECTRODEPOSITIONOF COPPER AND COPPER ALLOYS Frank Passal, Detroit, Mich., assignor to Metal and Thermit Corporation, Woodbridge Township, N.J., a corporation of New Jersey No Drawing. Application June 19, 1957 Serial No. 666,773

16 Claims. (Cl. 204- 44) as undercoats for subsequent electrodeposits, usually nickel and chromium. Alkaline-cyanide type baths are widely used for copper and copper alloy plating because of their relatively high plating speed, excellent throwing power and ease of maintenance. When plating from these baths, it has been found that anode current efliciencies are markedly lowered by anode polarization. Effective use has been made of relatively high anode current densities, e.g., current densities in the range up to about 20 amps. per square foot (a.s.f.) by adding tartrates and/or citrates to the bath. Although the'anode current etliciencies of these baths have been improved by the foregoing addition agents, they still tend to fall off rapidly as the current density is raised. The use of still higher current densities is. desirable provided the appreciable anode polarization is obviated, because the copper metal con. centration of the bath can be better maintained without rapid fluctuation; there is decreased tendency toward anodic oxidation of cyanide resulting in decreased cyanide consumption; and fewer copper anodes are required for a given installation. Effective plating utilizing these higher anode current densities has not been generally feasible because of the anode polarization and low current eificiencies obtained at the higher current densities when plating from conventional cyanide baths, even those containing citrate or tartrate additions.

I have now discovered improved alkaline-cyanide type baths from. which copper and copper alloys are electrodeposited at improved anode and cathode current efiiciencies in the lower current density range and at greatly improved current efiiciencies in the higher current density range.

It is an object of the present invention to provide an efficient and economical process for electrodepositing copper and copper alloy plates.

It is a further object of the present invention to provide improved baths for the electrodeposition of copper and copper alloys.

The invention also contemplates providing improved baths for the electrodepos-ition of copper.

Still another object of the invention is to provide irriproved baths for the electrodeposition of bronze.

The invention also contemplates providing improved baths for the electrodeposition of brass.

Other objects and advantages of the invention will be come apparent from the following description.

The present invention contemplates electrodepositing decorative and/ or protective copper or copper alloy plates from alkaline-cyanide baths containing at least 0.06 mole per liter of saccharate ion, -OOC(CHOH) COO--. The saccharate ionmay be incorporated by the addition tothe bath of a soluble saccharate compound. The cation of the soluble saccharatecompound should be one .that does not adversely afiect the propertiesor plating characteristics. of the bath. Preferred saccharatecompounds are the .alkali metalsaccharates,the.alkali metal acid saccharates, copper. saccharate and ammonium. .saccharate. The saccharateaddition in the form of the potassium and/orsodium salts or their acid salts, or mixtures thereof, is especially preferred. The saccharate additionmay also be made in the form of the mixed salts and particularly mixed sodium and potassium. saccharate. Saccharic acid, HOOC(CHOH) COOH, when added to cyanide baths may generate HCN, dependent. on the alkalinity of the bath. The acid addition may be safely made'to highly alkaline baths. The generation of some HCN by the acid addition to less alkaline baths may be tolerated if the addition is made under controlled conditions (slowly) and with good ventilation. To a lesser degree,"the use of the acid salts involves the same considerations.

Alkaline-cyanide baths containing as little as 0.06 mole per liter of a saccharate have improved anode current efiiciencies, particularly at higher current densities, 'as well as improved cathode current efficiencies. It is preferred that the baths contain between about 0.09 mole per liter and 0.24 moleper liter of the saccharate additive. In amounts greater than 0.24 mole per liter, the improved characteristics obtained do not usually justify the additional cost.

The plates electrodeposited from these baths are sound and generally smoothandfine-grained. The addition of saccharate to alkaline-cyanide plating baths improves the operating characteristics and deposits for all alkalinecyanide type copper and copper alloy plating baths. These generally include the following types of baths:

(1) Copper strike baths:

Copper g./l. About 15 Free potassium or sodium cyanide g./l. 1l-l5 Temperature F. 120-l4O Agitation Little or 'none Current density a.s.f. 10-50 (2) Intermediate speed baths:

Copper g./l. 30'- 3 8 Free potassium or sodium'cyanide g./ l. ..7 .5-15 Potassium or sodium hydroxide ....g./l. ..15-3 0 Potassium or sodium carbonate (optional) g./l About 15 Temperature F. Generally -180 Agitation Yes Current density a.s.f. 10-8 0 (3) Bright copper baths:

Copper g /l 37-75 Free potassium or sodium cyanide g./l 3.7-15 Potassium or sodium hydroxide g./l 15-30 Brightener, e.g., selenium bis diethyldithiocarbamate g./l About 0.004 Temperature F Generally 150-180 Agitation Yes Current density a.s.f 5-50 (4) Brass plating baths:

CuCN g /l 30-225 Zn(CN) g./l 9.4-11. Total NaCN g./l 56-425 Na CO g./l 30-123 Free NaCN g./l 30-225 Temperature F 70-100 C.D. (cathode) a.s.f 2-20 (5) Bronze plating baths:

Tin (as stannate) g./l 11-16 Copper g./l 18-30 Free KCN or NaCN tg./ 1-- "20-25 Temperature F 145-160 C.D. (cathode) a.s.f -100 I Equivalent amounts of potassium or sodium salts may be used. These baths and operating conditions are merely illustrative of plating from alkaline-cyanide type copper and copper alloy baths. Alkaline-cyanide baths and processes are described in Modern Electroplating, edited by A. G. Gray, pages 98-114 and 194-225 (1953). Electroplating from the bronze and brass plating baths illustrated may utilize the respective alloy anodes or copper anodes with periodic additions of the tin or zinc salts as they are deplenished.

The alkaline-cyanide bath may contain such primary brightening agents as the selenium and tellurium dithiocarbamates, e.g., selenium bis diethyldithiocarbamate; rhodanine; pseudothiohydantoin; 2,4 dioxothiazolidine; etc., alone or in conjunction with such secondary brighteners such as lead, zinc, bismuth, antimony salts, etc.

Conventional wetting agents of the kind generally used in alkaline-cyanide baths are also preferably incorporated in the bath. These include quaternary amine wetting agents such as C-decylbetaine, trimethylbenzylammonium chloride, or compounds such as alkyl S-arninopropionates, alkyl fi-iminodipropionates, alkyl polyoxyethylene glycol ethers, etc.

Best results are achieved when utilizing in the electrodeposition process a method of preventing the thin film immediately adjacent to the cathode from becoming depleted in metal ion content. This is conventionally accomplished by agitation e.g., solution pumping, cathode movement, air agitation etc., or by diffusion efiects, e.g., current interruption, periodic current reversal etc., or by combinations thereof. Superior results have been achieved by utilizing current interruption in conjunction with cathodemovernent. Anodes are conventionally not agitated.

For the purpose of providing a better understanding of the invention and a better appreciation of the advantages of the invention, the following illustrative examples are given.

EXAMPLE NO. 1

CuCN 60 g./l. KCN 90 g./l. KOH 22.5 g./I.

Potassium acid saccharate 22.5 g./l. (0.078 mole/1.).

EXAMPLE NO. 2

The bath of Example No. 1, using 22.5 g./l. Rochelle salts (potassium sodium tartrate) in place of the potassium acid saccharate.

Sound copper Was electrodeposited from the baths of Example Nos. 1 and 2. The operative conditions and resultant current efliciencies are given in Table I.

4 EXAMPLE NO. 3

CuCN 8 1-- 60 Free KCN g l 11.2 KOH g./l 22.5 Temp. F 150 (a) Potassium saccharate g./l 15 (b) Potassium sodium tartrate g./l 15 (c) No additive Control Table II Percent Anode Current Efficiencies C .D., a..s.f.

control tartrato saccharate This bath was also run with 60 g./l. additions of the above noted compounds (a) and (b).

EXAMPLE NO. 4

The bath using additives (a), (b), or (c) and operated at F., and F. with current densities of 10, 30 and 50 a.s.f., yields lustrous bronze deposits. The current efliciencies are high. The deposits are somewhat redder than deposits from baths of the same composition utilizing tartrates in place of saccharates, signifying a deposit containing more copper and less tin. This re-' sults from the greater copper current efliciency characteristics of the bath.

The excellent plating characteristics and the wide applicability of alkaline-cyanide copper-containing baths with saccharate additions is illustrated in these examples. Examples 1, 2 and 3 are furnished for comparative purposes. A study of the results in Tables I and II brings out the markedly improved anode and cathode current etficiencies achieved with baths containing the saccharate salt.

Additions of copper saccharate, ammonium saccharate, the other alkali metal (Li, Rb, Cs) saccharates, the alkali metal acid saccharates, and saccharic acid, when used in the foregoing baths, provide equally good electrodeposits with similarly improved current efiiciencies as do the potasssium and sodium salts.

The sound copper and copper alloy electrodeposits obtained from alkaline-cyanide type baths of the present invention are obtained on such conventional basis metals as iron, steel, nickel, zinc, lead, copper, etc., and alloys thereof. On certain basis metals such as iron or steel and zinc-base die-castings the basis metal is first given an initial thin flash of copper from a low efficiency cyanide copper bath.

As many embodiments of this invention may be made without departing from the spirit and scope thereof, it is to be understood that the invention includes all such modifications and variations as come within the scope of the appended claims.

- I claim:

' 1. An improved alkaline-cyanide bath for plating a metal selected from the class consisting of copper and copper base alloys which comprises copper cyanide, free cyanide and a small but effective amount not less than about 0.06 mole per liter of saccharate ion, said amount being sufiicient to improve the anode current efiiciency.

2. A bath as claimed in claim 1, said amount being between about 0.09 and about 0.24 mole per liter.

3. An improved alkaline-cyanide bath for plating a metal selected from the class consisting of copper and copper base alloys which comprises copper cyanide, free cyanide and a small but effective amount not less than about 0.06 mole per liter of at least one saccharate selected from the class consisting of alkali metal saccharates, alkali metal acid saccharates, copper saccharate, ammonium saccharate and saccharic acid, said amount being sufiicient to improve the anode current etficiency.

4. A bath as claimed in claim 3, said saccharate being potassium saccharate.

5. A bath as claimed in claim 3, said saccharate being ammonium saccharate.

6. A bath as claimed in claim 3, said saccharate being sodium saccharate.

7. A bath as claimed in claim 3, said saccharate being lithium saccharate.

8. A bath as claimed in claim 3, said saccharate being copper saccharate.

9. In a method of electrodepositing a metal selected from the class consisting of copper and copper base a1- loys, the step of depositing said metal from an alkalinecyanide bath comprising copper cyanide, free cyanide and a small but efiective amount not less than about 0.06 mole per liter of saccharate ion, said amount being suflicient to improve the anode current efliciency.

10. A method as claimed in claim 9, said amount being between about 0.09 and about 0.24 mole per liter.

11. In a method of electrodepositing a metal selected from the class consisting of copper and copper base alloys, the step of depositing said metal from an alkalinecyanide bath comprising copper cyanide, free cyanide and a small but effective amount not less than about 0.06 mole per liter of at least one saccharate selected from the class consisting of alkali metal saccharates, alkali metal acid saccharates, copper saccharate, ammonium saccharate and saccharic acid, said amount being sufficient to improve the anode current efliciency.

12. A method as claimed in claim 11, said saccharate being potassium saccharate.

13. A method as claimed in claim 11, said saccharate being ammonium saccharate.

14. A method as claimed in claim 11, said saccharate being sodium saccharate.

15. A method as claimed in claim 11, said saccharate being lithium saccharate.

16. A method as claimed in claim 11, said saccharate being copper saccharate.

References Cited in the file of this patent UNITED STATES PATENTS 694,658 Meurant Mar. 4, 1902 2,406,072 Gaver Aug. 20, 1946 2,443,600 Chester June 22, 1948 2,763,606 Hespenheide et a1 Sept. 18, 1956 

1. AN IMPROVED ALKALINE-CYANIDE BATH FOR PLATING A METAL SELECTED FROM THE CLASS CONSISTING OF COPPER AND COPPER BASE ALLOYS WHICH COMPRISES COPPER CYANIDE, FREE CYANIDE AND A SMALL BUT EFFECTIVE AMOUNT NOT LESS THAN ABOUT 0.06 MOLE PER LITER OF SACCHARATE ION, SAID AMOUNT BEING SUFFICIENT TO IMPROVE THE ANODE CURRENT EFFICIENT. 